Inner furnace air chamber

ABSTRACT

A furnace assembly and method in which an air-fuel mixture is supplied to a burner which is associated with at least one of the walls of the furnace assembly with an auxiliarly supply of air being discharged toward said burner for mixing and combusting with the unburnt fuel from the burner.

a 7 limited States Fatwa 1 1 3,865,084 De Paister 1 Feb. 11, 11975 4]INNER FURNACE AFR CHAMBER 2,022,512 11/1935 Macchi 431/10 X 1 InventDavid De Power, Morristown, 5:31;??? 2/1332 1132.?7111131113331111:311333131 33141? NJ. 3,699,903 10/1972 King 110/28 X [73] Assignee:Foster Wheeler Corporation,

L'vmgswn Primary EXaminer-Kenneth W. Slprague 22 Filed; 7 1974 Attorney,Agent, or Firm-Marvin A. Naigur; John E.

Wilson [21] App]. No.: 431,243

[52] US. Cl. 122/235 B, 110/1 K, 110/28 R, [57] ABSTRACT 110/75 R,431/10 [51] Km. C1. F22b A furnace assembly and method In which air-fuel53 Field f Search 0/1 K 23 R, 23 A 23 F, mixture is supplied to a burnerwhich is associated 0 2 122 235 R, 235 431 0; 119 72 with at least oneof the walls of the furnace assembly R, 75 R, K, J with an auxiliarlysupply of air being discharged toward said burner for mixing andcombusting with the 5 R f r Cited unburnt fuel from the burner.

UNITED STATES PATENTS 5 Claims, 3 Drawing Figures 1,889,031 11/1932 Bell122/235 X e4 M w l2\ L82 Mg)-l H!74 4o 24 1 1 .1 g 24 4 ;I

@f ea-{a 4 -Tif 6* -LQ. J Z: 54 $3 *1: 1 42 -41 To ::5; i2 I 1PATENTEDFEBI H875 SHEET '2 OF 2 FIG. 2.

INNER FURNACE AIR CHAMBER BACKGROUND OF THE INVENTION This inventionrelates to a furnace assembly and method and, more particularly, to animproved furnace assembly and method in which the formation of nitricoxides as a result of fuel combustion is reduced.

A great deal of attention has recently been directed to the reduction ofnitric oxides resulting from the combustion of fuel at burners, andespecially in connection with the furnace sections of relatively largeinstallations such as vapor generators and the like.

In these type of arrangements, one or more burners are usually disposedin communication with the interior of the furnace and operate to combusteither oil or gas in air. Since nitrogen is present in the air and, inmost cases, in the fuel, a relatively high level of nitric oxide, ornitric oxides, are produced which causes severe air pollution problems.

Since the formation of nitric oxides increases with increases in theburner temperatures, several attempts have been made to suppress thelatter temperatures and thus reduce the formation of nitric oxides.However, previous attempts have often resulted in added expense in termsof costs, etc., and lead to other related problems.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide a furnace assembly and method in which the level ofnitric oxides is considerably reduced.

It is a more specific object of the present invention to provide afurnace assembly and method in which a two-stage combustion process isachieved which lowers the flame temperature in order to reduce theformation of nitric oxides.

Toward the fulfillment ofthese and other objects, the furnace assemblyof the present invention comprises a housing formed by a plurality ofinterconnected walls, at least one burner associated with at least oneof said walls, means for supplying an air-fuel mixture to said burnerfor combusting in said furnace, and means disposed within said housingand in a spaced relation to said walls for discharging air towards saidburner for mixing and combusting with the unburnt fuel from said burner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view depictingthe furnace assembly of the present invention shown in conjunction witha vapor generator;

FIG. 2 is an enlarged cross-sectional view taken along the line 22 ofFIG. 1; and

FIG. 3 is an enlarged partial elevational view ofa portion of thefurnace assembly of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2 ofthe drawings, a furnace incorporating features of the present inventionis shown in general by the reference numeral as installed in a vaporgenerator 12. The furnace I0 is rectangular shaped, elongated, andextends from a bottom hopper portion 14 to an upper outlet area 16 whichis enclosed by a penthouse 18 for the vapor generator 12.

The vapor generator 12 includes a convection section 20 which has aninlet portion enclosed by the penthouse 18 and an outlet portionconnected to an air heater 22 to be described in detail later.

The furnace 10 is formed by front and rear walls 24 and 26,respectively, and a pair of side walls 28 and 30. As shown in FIG. 3 inconnection with the wall 24, the walls are formed by welding together aplurality of tinned tubes 32 along their lengths so that the enclosureformed by the walls is substantially gas tight. In a normal installationan insulating wall of a suitable insulating material would be providedadjacent each of the walls 24, 26, 28, and 30 and externally thereof.However, for the convenience of presentation these insulating walls havebeen omitted from the present drawings.

Water is passed through the tubes 32 of the walls 24, 26, 28 and 30 andis routed in a. predetermined flow path by means of suitable headers,downcomers, etc., in a manner so that it is gradually turned into steamby virtue of the heat generated in the furnace 10, after which the steamis superheated and collected in drums or the like in a conventionalmanner. Hot gases flowing upwardly in the furnace 10 exit through theoutlet area 16 and pass downwardly through the convection section 20 andinto the air heater 22 for further treatment in a manner to be describedin detail later.

A windbox 40 encloses the lower portion of the furnace 10 for supplyingair to the furnace. The windbox 40 includes front and rear walls 412 and44, which are spaced from the walls 24 and 26, respectively, of thefurnace 10. A plurality of burners, shown in general by the referencenumeral 46, are supported by the windbox 40 and discharge throughopenings formed in the walls 24 and 26.

The burners 46 associated with the front wall 24 of the furnace 10 areshown in detail in FIG. 3. In particular, the burners 46 are supportedby the wall 42 of the windbox 40 and are shown as being arranged in twovertical walls of four burners per row, it being understood that thenumber of burners 46 and their particular pattern can vary. Since theburners 46 are of a conventional design and form no portion of thepresent invention, they are shown only in general with it beingunderstood that they include an inlet for receiving fuel, which can bein liquid or gaseous form or which can be a mixture of pulverized coaland primary air. A series of openings 48 are formed through the wall 24in alignment with the burners 46 for allowing air from the windbox 40 topass into the furnace 10 where it combines with the fuel from theburners 46 which, upon ignition, combusts in a primary combustion zoneformed in the interior of the furnace immediately adjacent the openings48, in a conventional manner.

Air from an external source (not shown) is introduced to the systemthrough a duct 50 with a portion of it passing into the air heater 22which is adapted to effect a heat exchange between the latter air andthe combustion gases from the convection section 20 in a conventionalmanner. These gases, after passing through the air heater 22, dischargevia a duct 54 to a stack, or the like, while the heated air dischargingfrom the air heater 22 is routed through a duct 56 and into the lowerportion of the windbox 40 for passage through the openings 48. The duct56 has a venturi portion for the purpose of measuring the amount of airflow,.which flow is regulated by means of a damper 58 formed in the duct56 downstream of its venturi portion.

According to a main feature of the present invention, a quantity ofsupplemental air is discharged directly toward the burner openings 48 inthe walls 24 and 26 which aids in reducing the formation of nitricoxides. To this end, an enclosure 60 is provided within the furnace land is formed by four interconnected walls 62, 64, 66, and 68 each ofwhich are formed by a plurality of interconnected finned tubes similarto the walls 24, 26, 28, and 30 of the furnace 10.

A plurality of openings 70 are formed through the walls 62 and 64 of theenclosure 60 with a portion of the openings being located directlyopposite corresponding openings 48 formed in the walls 24 and 26 of thefurnace assembly 10. Although only the walls 24 and 62 of the furnace 12and the enclosure 60 are shown in detail in FIG. 2, it is understoodthat the Walls 26 and 64, respectively, are formed identically.

As shown in FIG. 1, the finned tubes forming the walls of the enclosure60 are connected to upper headers 74 and lower headers 76, it beingunderstood that downcomers, etc., can also be provided to route waterthrough the walls in a manner to generate steam and pass same into thesteam drum, or the like, which also serves the main system.

The air duct 50 is also connected, via ducts 80, 82 and 84, to theenclosure 60 to supply air to the latter enclosure for discharge throughthe openings '70 provided in the walls 62 and 64. A damper 86 isprovided in the duct 80 to regulate the quantity of air supplied to theenclosure 70.

In operation, the amount of air supplied to the wind box 40 via the duct56 is regulated by the damper 58 so that it is less than the theoreticalcombustion air requirements for the fuel supplied to the burners 46.This delays the complete combustion of the fuel in the primarycombustion zones located in the furnace l0 adjacent the openings 48, andresults in a relatively low flame temperature, which reduces theformation of nitric oxides. The amount of air supplied by the enclosure60 via the openings 70 is regulated by the damper 86 to insure that itis sufficient to combust the remaining unburnt fuel from the burners 46in a secondary combustion zone formed between the openings 48 and theopenings 70. Since the openings 70 are aligned with the openings 48 andsince air from the enclosure 60 is discharged in a direction directlyopposite that of the fuelair mixture from the burners 46, it can beappreciated that optimum mixing occurs between the respective fluids tofacilitate complete combustion of the unburnt fuel with a minimumquantity of excess air from the enclosure 60.

The water passing through the walls 62, 64, 66, and 68 of the enclosure60 maintains the enclosure at a relatively low temperature to protect itfrom damage, and, in addition, cools the flame temperature at thesecondary combustion zone.

It is noted from a view of FIG. 1 that a portion of the openings 70extend above the upper burners 46 to insure that air is available to mixwith any unburnt fuel rising towards the top of the furnace by naturalconvection.

Of course, other variations of the specific construction and arrangementof the furnace assembly disclosed above can be made by those skilled inthe art without departing from the invention as defined in the appendedclaims.

What is claimed is:

1. A furnace assembly comprising a housing formed by a plurality ofinterconnected walls, a plurality of burners associated with at leastone of said walls, means for supplying an air-fuel mixture to saidburners for combusting in said housing, an enclosure extending withinsaid housing and formed by interconnected walls, a wall of saidenclosure extending parallel to said one wall of said housing and havinga plurality of openings respectively facing said burners, said latterenclosure wall being formed by a plurality of interconnected finnedtubes, and means for supplying air to said enclosure for dischargingthrough said openings and towards said burners for mixing and combustingwith the unburnt fuel from said burners, and means for passing waterthrough said tubes to cool said tubes and the air discharging throughsaid openings.

2. The furnace assembly of claim 1 wherein the walls or said housing areformed by a plurality of interconnected finned tubes for receiving waterto be heated by said furnace.

3. The furnace assembly of claim 1 wherein the air portion of saidair-fuel mixture is less than that required to achieve completecombustion and wherein the air discharged through said openings issufficient to achieve complete combustion.

4. A method of burning a fuel air mixture in a furnace to produce aminimum amount of nitrogen oxides in the combustion gases leaving thefurnace, which comprises the steps of introducing the fuel into thefurnace through a burner port in a furnace wall, introducing a portionof the combustion air into said furnace through said burner port inmixing relationship with said fuel, regulating the amount of airsupplied through said burner port to an amount which is less than thetheoretical combustion air requirements for the corresponding fuel todelay the complete combustion of said fuel and thereby reduce themaximum flame temperature in the furnace and the formation of nitrogenoxides below the values which would occur if all of the air required forcomplete combustion were introduced with the fuel, discharging theremaining amount of air required to insure complete combustion of thefuel through openings extending through a wall of an enclosure disposedwithin said furnace, said remaining amount of air being directed towardssaid burner port and in a direction opposite the direction of dischargeof said fuel and air so as to mix said remaining amount of air with theunburnt portion of said fuel to complete the combustion of said fuel,and cooling the wall of said enclosure through which said openingsextend to cool said remaining amount of air.

5. The method of claim 4 wherein said wall of said enclosure is formedby a plurality of interconnected finned tubes, said step of coolingcomprising the step of passing water through said tubes.

1. A furnace assembly comprising a housing formed by a plurality ofinterconnected walls, a plurality of burners associated with at leastone of said walls, means for supplying an air-fuel mixture to saidburners for combusting in said housing, an enclosure extending withinsaid housing and formed by interconnected walls, a wall of saidenclosure extending parallel to said one wall of said housing and havinga plurality of openings respectively facing said burners, said latterenclosure wall being formed by a plurality of interconnected finnedtubes, and means for supplying air to said enclosure for dischargingthrough said openings and towards said burners for mixing and combustingwith the unburnt fuel from said burners, and means for passing waterthrough said tubes to cool said tubes and the air discharging throughsaid openings.
 2. The furnace assembly of claim 1 wherein the walls orsaid housing are formed by a plurality of interconnected finned tubesfor receiving water to be heated by said furnace.
 3. The furnaceassembly of claim 1 wherein the air portion of said air-fuel mixture isless than that required to achieve complete combustion and wherein theair discharged through said openings is sufficient to achieve completecombustion.
 4. A method of burning a fUel-air mixture in a furnace toproduce a minimum amount of nitrogen oxides in the combustion gasesleaving the furnace, which comprises the steps of introducing the fuelinto the furnace through a burner port in a furnace wall, introducing aportion of the combustion air into said furnace through said burner portin mixing relationship with said fuel, regulating the amount of airsupplied through said burner port to an amount which is less than thetheoretical combustion air requirements for the corresponding fuel todelay the complete combustion of said fuel and thereby reduce themaximum flame temperature in the furnace and the formation of nitrogenoxides below the values which would occur if all of the air required forcomplete combustion were introduced with the fuel, discharging theremaining amount of air required to insure complete combustion of thefuel through openings extending through a wall of an enclosure disposedwithin said furnace, said remaining amount of air being directed towardssaid burner port and in a direction opposite the direction of dischargeof said fuel and air so as to mix said remaining amount of air with theunburnt portion of said fuel to complete the combustion of said fuel,and cooling the wall of said enclosure through which said openingsextend to cool said remaining amount of air.
 5. The method of claim 4wherein said wall of said enclosure is formed by a plurality ofinterconnected finned tubes, said step of cooling comprising the step ofpassing water through said tubes.